As a liquid emitting device, there is an ink jet printer apparatus in which a recording liquid, or a so-called ink, is emitted via an ink emitting head to a recording paper sheet, as a support, to record an image or a letter/character thereon. The printer apparatus of the ink jet system has advantages such as low running costs, small size, and ease in printing a colored image.
The ink jet system, emitting the ink via an ink emitting head, may be implemented by, for example, a deflection system, a cavity system, a thermo-jet system, a bubble-jet system (registered trademark), thermal ink jet system, a slit jet system, or a spark jet system. Based on these various operating principles, the ink is turned into fine liquid droplets, which are then emitted via emitting openings, that is, nozzles, of an ink emitting head, so as to be deposited on the sheet for recording an image or a letter/character thereon.
Meanwhile, a demand is raised for the nozzles not to be stopped up with the recorded liquid used in the ink jet recording system. It has so far been felt that fine bubbles in the ink represent one of the factors possibly responsible for nozzle clogging.
In the ink, a preset quantity of a gas, such as air, remains dissolved. If, with rise in temperature, the gas is lowered in solubility, the gas which may not be dissolved in the liquid is separated to form fine bubbles in the liquid. Specifically, when the ink present in an ink tank adapted for supplying the ink to e.g. an ink emitting head, in an ink duct or in an ink emitting duct rises in temperature, the gas dissolved in the liquid is released to form fine bubbles.
When these fine bubbles are present in the ink emitting head, emission troubles, such as non-emission of the ink from the nozzle or warped emission of the ink, that is, the ink being emitted from the nozzle along a path offset from the intended path, are produced, with the result that printed image suffers from white spots or becomes blurred to degrade the printing quality.
In the recording system in which the ink is turned into fine liquid droplets, under the action of thermal energy, and the so formed liquid droplets are emitted from the nozzle, that is, in the recording system of the thermal type or the bubble jet type, the ink is heated rapidly by a heater and emitted in the form of liquid droplets under the pressure of air bubbles generated by film boiling of the ink. Thus, heat is accumulated in the vicinity of the heater, and hence the ink in the ink duct is extremely liable to be raised in temperature, with the result that emission troubles, such as the aforementioned non-emission or warped emission, tend to be produced to a pronounced extent.
For combating such problem, it is proposed in e.g. the JP Patent Publications 1 and 2 to use an aqueous pigment ink doped with a propylene oxide adduct polymer of lower alcohol. However, these proposals are not up to sufficient suppression of fine bubbles and further improvement has been desired.
It has also been proposed in Patent Publication 3 to add an ethylene oxide adduct of a higher dehydrate alcohol alkoxylate in an aqueous pigment ink. The ink proposed in this Patent Publication 3 is alleged to be superior in emission stability during high frequency driving, penetrability to the recording paper sheet and in drying properties. However, if a compound obtained on adding only ethylene oxide to the higher alcohol a dihydric alcohol alkoxylate is contained in the ink, in association with the teaching by Patent Publication 1, it has not been possible to cope successfully with the problem of the nozzles being stopped with fine bubbles. Specifically, the ink obtained on adding 7 mol or more only of ethylene oxide undergoes vigorous foaming to cause severe nozzle clogging.
On the other hand, with the ink used for the ink jet recording system, a demand has been raised not only for prohibiting nozzle clogging but also for preventing the optical density from being lowered or for preventing the boundary bleeding or speckled color mixing in all-over printing, even in case of printing on a medium grade paper sheet, such as copy paper sheet or report paper sheet, or a high grade paper sheet.
For meeting the demand, it has been proposed in e.g. Patent Publication 4 to use a compound, obtained on treating a water-insoluble colorant with a high polymer material containing a sulfonic acid (sulfonate) group and/or with a high polymer material containing phosphoric acid (phosphate) group, as a colorant, and also to add a high polymer material, including a carboxylic acid (carboxylate) to the ink. It has also been proposed in Patent Publication 5 to get the ink doped with an alginic acid having a D-mannuronic acid to L-guluronic acid ratio ranging between 0.5 and 1.2. It has also been proposed in Patent Publication 6 to add at least one surfactant selected from the group of fluorine-based surfactants and silicon-based surfactants and alginates to the ink. However, neither of these Publications is sufficient to meet the aforementioned demand and further improvement has been desired.
On the other hand, the aforementioned problem, related with the bubbles, occurs more pronouncedly with a printer apparatus capable of performing high-speed printing on a recording paper sheet, that is, a line-based printer apparatus having an ink emitting range substantially equal to the width of the recording paper sheet (for example, see Patent Publications 7 to 9).
More specifically, with a line-based printer apparatus, having one or more rows of nozzles juxtaposed in a direction substantially at right angles to the width-wise direction of the recording paper sheet, as distinct from a serial-based printer apparatus in which an ink emitting head is scanned in a direction substantially at right angles to the feed direction of the recording paper sheet, an ink duct for conducting the ink from an ink tank is formed for traversing the feed direction of the recording paper sheet, and in which a plural number of ink emitting heads, each having a nozzle, are arrayed on one or both sides of the ink duct, the number of ink heating sites is correspondingly increased with the number of the nozzles, so that fine bubbles tend to be generated. Moreover, the ink tank is separated from the ink emitting head a long distance, whilst the structure from the ink tank to the ink emitting head is complicated to render it difficult to remove the fine bubbles generated, with the result that inconveniences ascribable to the fine bubbles occur most pronouncedly.
With the line-based printer apparatus, the period of emission of liquid droplets from one nozzle line to the next is that short and hence an ink exhibiting superior penetration characteristics into the recording paper sheet needs to be used. If the ink of this sort is used for a paper sheet of medium quality, the ink exhibits the tendency to seep into the paper sheet along its depth, that is, along its thickness, with the result that the optical density tends to be lowered.
In addition, if so-called color printing of emitting inks of different colors on a recording paper sheet, is to be carried out with the line-based printer apparatus, where the period of emission of liquid droplets from one nozzle line to the next is short, a color liquid droplet is deposited before the previously deposited color liquid droplet sufficiently seeps into the bulk part of the paper sheet, with the consequence that boundary bleeding or speckled color mixing in all-over printing tends to be produced between different colors.    Patent Publication 1: Japanese Laid-Open Patent publication 2001-2964    Patent Publication 2: Japanese Laid-Open Patent publication H10-46075    Patent Publication 3: Japanese Laid-Open Patent publication H7-70491    Patent Publication 4: Japanese Laid-Open Patent publication 2000-154342    Patent Publication 5: Japanese Laid-Open Patent publication H8-290656    Patent Publication 6: Japanese Laid-Open Patent publication H8-193177    Patent Publication 7: Japanese Laid-Open Patent publication 2002-36522    Patent Publication 8: Japanese Laid-Open Patent publication 2001-315385    Patent Publication 9: Japanese Laid-Open Patent publication 2001-301199